RECENT PRESENTATIONS

Nichols, E.A., Ilan, A.B., Smith, M.E. & Gevins, A. (2001) Effects of Marijuana on Neurophysiological Correlates of Working and Intermediate- Term Memory. Annual Meeting of Society for Neuroscience Conference. November, San Diego.

ABSTRACT

Cannabinoid receptors are abundant in the frontal cortex and hippocampus, areas crucial for attentional control, working memory (WM), and the creation of more lasting memories. Although knowledge of marijuana's neurobiological effects has proliferated, research on marijuana's impact on human cognitive brain function has not progressed as quickly. To examine marijuana's effects on neurophysiological measures of working and recent memory, a double-blind, counterbalanced study was performed in which 40-channel EEG recordings were obtained from N=10 casual marijuana users before and after smoking active (3.45% THC) or placebo (0.006% THC) marijuana. A spatial N-back task was used to measure WM ability. Intermediate-term memory over a period of 5-10 minutes was measured with a word recognition task. Objective and subjective measures of intoxication increased after smoking marijuana, but alertness and motivation were unchanged. After smoking marijuana reaction time in the WM task increased, as did EEG alpha (8-11 Hz) power, a signal inversely proportional to task-related cortical activation. Amplitudes of the N1 and P3 event-related potentials (ERPs) were attenuated, implying a reduction in attentional resources allocated to task performance after marijuana smoking. Marijuana slowed responses in the word recognition task, decreased subjects' ability to discriminate previously studied "old" words from distractors, and decreased the amplitude of the N1 and the ERP slow wave, suggesting an impairment in memory for recent events. The results indicate that marijuana has profound effects on neurophysiological systems regulating WM and delayed recognition.